It is known that the deconfining transition of QCD is accompanied by
the appearance of localized eigenmodes at the low end of the Dirac spectrum. In the quenched case localization appears exactly at the critical temperature of deconfinement. In the present work, using quenched simulations exactly at the critical temperature, we show that the localization properties of low Dirac modes change abruptly between the confined and deconfined phase. This means that in the real Polyakov loop sector, the mobility edge has a discontinuity at the critical temperature. In contrast, in the complex sector, there is no such discontinuity at $T_c$, even the lowest Dirac modes remain localized at the critical temperature in the deconfined phase.